1. Technical Field
The present invention relates to a bottle-shaped container made of thermoplastic resin, and intends to advantageously avoid lowering of the mechanical strength due to a light-weighted or thin-walled nature of the container.
2. Related Art
Synthetic resin containers, such as PET bottles, have been widely used as containers, e.g., for filling therein foods, beverages, cosmetics or medicines since such containers are light in weight and can thus be easily handled, have transparency to exhibit a refined appearance comparable to glass containers, and can be produced at low cost.
Synthetic resin containers have a relatively low mechanical strength against external forces. Therefore, when the container is gripped at its main body portion for pouring the contents out of the container, the container inevitably undergoes deformation at its gripped part.
It is thus a typical countermeasure to appropriately control the container wall thickness and form longitudinal ribs, lateral ribs or waists (i.e., circumferential grooves surrounding the main body portion) so as to improve the resistances of the container to external forces, such as rigidity, buckling strength, etc.
However, there is an increasing demand for thin-walled (or light-weighted) containers so as to reduce the resin amount to be used per one container from a standpoint of effective utilization of resources and reduction in the amount of wastes, resulting in a situation where the strength of the container is inevitably further lowered to deal with such a demand.
Particularly, in connection with PET bottles having a filling volume of about 500 milliliters, various kinds of commercial products have been recently increasingly sold by vending machines. In this instance, when such a bottle is light-weighted, there tends to be caused troubles wherein recesses are formed on the bottle at its lateral side (particularly, at its shoulder portion) due to an impact caused by dropping of the bottles from the storage down to the outlets, via chutes of the vending machines.